#include <bits/stdc++.h>
using namespace std;

int main()
{
    int n;
    cin >> n;
    int r = 0, pas = 1 << 19;
    while(pas)
    {
        if(r + pas <= n)
        {
            cout << "? " << r + pas << endl;
            int x;
            cin >> x;
            if(x == 0)
                r += pas;
        }
        pas /= 2;
    }
    cout << "! " << r + 1 << endl;
    return 0;
}